This one's got me a little baffled. Maybe someone can help.
First, they're a Canadian band singing about America. From the chorus, there appears to be some sympathy and admiration, but the rest of the lyrics tend to point to the moral sickness that pervades our country. The condition described in the chorus is a result of this moral sickness. For example the succession of Roman emperors: Marcus Aurelius is remembered for his pur platonic virtue as the ideal emperor; Trajan Decius is an obscure entity much later; followed by Constantine, who ruined Christianity by making it easy. It then became a State religion, complete with politicl vying, wealth, and corruption--probably the worst thing that ever happened to obscur "the Way."
Some of the lines are a little confusing, especially the last stanza (is it complementary to America or maybe our Savior?), but overall the meaning has to be our self-dilusion that we're something that we're not. We've lost our way through materialism and moral bankruptcy and won't learn through the window of history, and as a result we're hurting.